1. Field of the Invention
This invention relates to formulated lubricating oil products exhibiting resistance to oxidation through the use of additives.
2. Description of the Invention
The present invention is a lubricating formulation exhibiting enhanced resistance to oxidation, said formulation comprising a major amount of an oil of lubricating viscosity and a minor amount of additives comprising a combination of phenyl naphthyl amine, one or more dimercaptothiadiazoles or derivative thereof, one or more triazoles or benzotriazoles of derivative thereof, but in the absence of diphenyl amine or diamine antioxidants, and to a method for enhancing the oxidation resistance of formulated oils, which do not contain diphenyl amine or diamine antioxidants, by the addition to such oils of a minor amount of a combination of phenyl naphthyl amine, one or more dimercaptothiadiazoles or derivative thereof, and one or more triazoles or benzotriazoles or derivative thereof.
The base oil of lubricating viscosity can be any natural or synthetic base oil, including those derived from paraffinic or naphthenic crude oils, tar sands, shale oil, coal oil, and processed using standard refinery techniques. These may include fractionated distillation, solvent or catalyst dewaxing of raffinate products, solvent extraction of aromatics, hydrotreating, oils produced by severe hydrotreating or hydroprocessing to reduce aromatic and/or olefinic hydrocarbon content, as well as to reduce sulfur and nitrogen content, isomerization of waxy raffinates, etc.
Synthetic oils include oils of the lubricating oil boiling range derived from a Fischer-Tropsch hydrocarbon synthesis process, or from the isomerization of petroleum wax or Fischer-Tropsch synthetic wax, as well as polyalphaolefins, which are hydrogenated oligomers of C.sub.2 -C.sub.16 alpha olefins.
The lubricating oil formulation contains a minor amount of additive materials, comprising a phenyl naphthyl amine per se, one or more triazoles, benzotriazoles or derivatives thereof, and one or more dimercaptothiodiazoles or derivatives thereof.
The phenyl naphthyl amine is unsubstituted by any hydrocarbyl group such as alkyl, aryl, or alkaryl group, being substantially just phenyl naphthyl amine (either phenyl alpha naphthyl amine or phenyl beta naphthyl amine).
The amount of phenyl naphthyl amine used ranges from about 0.05 to 1.0 wt %, preferably about 0.3 to 0.8 wt % (active ingredient).
The dimercaptothiadiazole or derivative thereof is represented by the general formula: ##STR1##
wherein R.sub.1 and R.sub.2 are the same or different, and are selected from hydrogen, C.sub.1 -C.sub.20 hydrocarbyl, or C.sub.1 -C.sub.20 alkyl (wherein at least one of R.sub.1 or R.sub.2 is not hydrogen), and x and y are the same or different integers ranging from 1 to 5, preferably 1 to 2, or mixtures of such materials.
The dimercaptothiadiazole is used in an amount in the range 0.001 to 0.5 wt %, preferably 0.01 to 0.10 wt %.
Benzotriazole or derivative thereof is represented by the general formula: ##STR2##
wherein R.sub.4 is hydrogen or C.sub.1 -C.sub.10 alkyl, preferably hydrogen or C.sub.1 -C.sub.2 alkyl, and x is an integer ranging from 1 to 4, preferably 1; and R.sub.5 and R.sub.6 are hydrocarbyl, commonly 2-ethylhexyl, or other substantially hydrocarbyl. Closely related triazole derivatives represented by the structures below, are also commonly used as substitutes for benzotriazole derivatives in lubricating oils, where R.sub.11 and R.sub.12 are hydrocarbyl, commonly 2-ethylhexyl, or other substantially hydrocarbyl. ##STR3##
The triazole or benzotriazole and/or derivative thereof is used in an amount in the range 0.005 to 0.5 wt %, preferably 0.01 to 0.20 wt % (active ingredient).
The lubricating oil containing the three above recited additive components in combination may also contain other typical lubricant additives, including other antioxidants of the phenolic and/or aminic type, pour point depressants such as poly(meth)acrylates, ethylene/vinyl acetate copolymers, acetate/fumarate copolymers, etc., antiwear/extreme pressure additives such as hydrocarbyl substituted phosphate esters, sulfur containing compounds such as metal or non-metal hydrocarbyl dithiophosphates, or dithiocarbamates, e.g., ZDDP, or sulphurised olefins or esters, rust inhibitor agents, including alkyl succinimides and derivatives thereof, and/or carboxylic acids or their partially or fully esterified derivatives, and/or sulfonates, and/or partially oxidised hydrocarbons, etc., demulsifiers, antifoamants, dyes, etc. The amounts of such additional additives used, if any, is left to the discretion of the practitioner in response to his own formulation requirements.